From 78b7d9af26ae802b3ca0d7b794b366ab4d515647 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eugenio=20P=C3=A9rez?= <eperezma@redhat.com>
Date: Tue, 23 Aug 2022 20:30:27 +0200
Subject: [PATCH 12/23] vhost: use SVQ element ndescs instead of opaque data
 for desc validation
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RH-Author: Eugenio Pérez <eperezma@redhat.com>
RH-MergeRequest: 116: vdpa: Restore device state on destination
RH-Bugzilla: 2114060
RH-Acked-by: Cindy Lu <lulu@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Commit: [11/21] 536ba65ff7241c4dc66362294ba8de4354260d6f (eperezmartin/qemu-kvm)
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2114060
Upstream status: git@github.com:jasowang/qemu.git net-next

Since we're going to allow SVQ to add elements without the guest's
knowledge and without its own VirtQueueElement, it's easier to check if
an element is a valid head checking a different thing than the
VirtQueueElement.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 70e0841722deb363b53cdcd465af12a0d1461b60)
---
 hw/virtio/vhost-shadow-virtqueue.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 2ae47d90a1..7792f3db1d 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -414,7 +414,7 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
         return NULL;
     }
 
-    if (unlikely(!svq->desc_state[used_elem.id].elem)) {
+    if (unlikely(!svq->desc_state[used_elem.id].ndescs)) {
         qemu_log_mask(LOG_GUEST_ERROR,
             "Device %s says index %u is used, but it was not available",
             svq->vdev->name, used_elem.id);
@@ -422,6 +422,7 @@ static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
     }
 
     num = svq->desc_state[used_elem.id].ndescs;
+    svq->desc_state[used_elem.id].ndescs = 0;
     last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
     svq->desc_next[last_used_chain] = svq->free_head;
     svq->free_head = used_elem.id;
-- 
2.31.1